1. Field of the Invention
The present invention relates to an imaging lens which is suitably used in a vehicle camera, a surveillance camera, a camera for a portable telephone, or the like, and which forms an optical image on a solid-state imaging device, and also relates to a camera apparatus comprising the lens.
2. Description of Related Art
A vehicle camera for imaging the surrounding of a vehicle is known (for example, see JP-A-2006-168683). Such vehicle cameras include: an out-vehicle camera which is disposed outside a vehicle, and which images, for example, a blind zone of the driver's vision to assist the driving operation; and an in-vehicle camera which images a field of view identical with the driver's vision field in order to record the status of occurrence of a traffic accident or the like. In accordance with enhancement of performance and cost reduction of a solid-state imaging device, recently, vehicles having a vehicle camera are becoming popular.
Among imaging lenses in the background art, an imaging lens disclosed in JP-A-2001-337268 comprises a first lens which is a meniscus lens having a negative refractive power, and positive second and third lenses, sequentially from the object side. All the surfaces other than the object-side surface of the first lens are formed as an aspherical surface, so that excellent telecentricity and a wide field angle are realized. An imaging lens disclosed in JP-A-2005-181596 comprises a first lens which is a meniscus spherical glass lens having a negative refractive power, and second and third lenses which are aspherical plastic lenses having positive refractive powers, and realizes the brightness of F 2.6 and a wide field angle of 80 degree or more. An imaging lens disclosed in JP-A-2005-321742 is configured by three plastic lenses in which the surface closest to the object side is a spherical surface, and the other surfaces are formed as an aspherical surface, and realizes the brightness of F 2.96 and a wide field angle of 150 degree or more. Endoscope imaging lenses disclosed in Japanese Patent No. 3206930 and JP-A-10-170821 comprise a plano-concave lens and two positive lenses sequentially from the object side, and simultaneously realize excellent telecentricity and compactness.
However, the imaging lenses disclosed in JP-A-2001-337268, JP-A-2005-181596 and JP-A-2005-321742 are insufficient in miniaturization. The imaging lens disclosed in Japanese Patent No. 3206930 uses high-refractive index glass as the first lens, and hence has a disadvantage that the cost is high. The imaging lens disclosed in JP-A-10-170821 has the F-number of 3.8 or more, and hence is dark. Therefore, the imaging lens is not suitable for use in a vehicle camera, surveillance camera, or the like which is not always used in an environment of adequate brightness.